class Counter{
    public int count;

    //可重入
    public synchronized void add(){
        synchronized (this) {
            count++;
        }
    }
}
public class demo1 {
    public static void main(String[] args) throws InterruptedException {
        Counter counter = new Counter();
        Thread t1 = new Thread(() -> {
            for (int i = 0; i < 5000; i++) {
                counter.add();
            }
        });
        Thread t2 = new Thread(() -> {
            for (int i = 0; i < 5000; i++) {
                counter.add();
            }
        });
        t1.start();
        t2.start();

        t1.join();
        t2.join();
        System.out.println(counter.count);
    }
}
